1. Field
The present invention in general pertains to light emitting apparatus such as flashlights, spotlights, reading lights, etc. of the type having means for light modulation which varies the color and intensity or brightness of an incident beam of light produced by the apparatus. In particular, the present invention pertains to a novel inexpensive means for light modulation by varying the optical density and color emitted by the light emitting apparatus using a variable density filter system which is manually operated and which incorporates a pair of synthetic linear polarizing filters (polarizers) that produce an incident polarized beam of light where extreme or very high extinction density is required.
2. State of the Art
In many situations it would be highly advantageous to have a device for emitting an incident beam of light, such as a reading light, flashlight, or spotlight which could be quickly and easily adjusted by simple manual manipulation of a dial, knob, lens etc., so as to control the intensity or brightness of the incident beam of light produced by the device over a broad range from maximum intensity to a very subdued intensity approaching almost total extinction. Military flashlights are often supplied with a set of lenses including a clear lens, an opaque lens and one or more colored lenses. The lens cap of the flashlight must be removed and the lenses changed when a different color or change in opacity is desired opacity. This is a tedious, time consuming operation, and the various lenses of the set of lenses are easily misplaced and lost. Relatively costly circuitry can be incorporated into the flashlight or spotlight to effectively control the intensity of the incident beam of light produced by the flashlight by varying the voltage applied to the lamp. Such circuitry is prone to wear and premature failure in addition to being costly.
Polarized filters, hereinafter referred to as lenses, have been used to filter light. In U.S. Pat. Nos. 2,705,318 and 3,511,211 it is proposed to use polarized lenses in instrument panel dials in aircraft and automobiles to control the illumination of the gauges in the instrument panel. The light from the polarized lenses illuminates transparent indicia on a dial which is located in close proximity to the polarized lenses. There is no suggestion that the light passing through the polarized lenses could be projected as an incident beam of light to illuminate specific objects at a considerable distance from the polarized lenses. In U.S. Pat. No. 2,263,684 a safe light for use in handling photographic materials is disclosed in which polarized lenses are used to control the intensity of emitted light. The light in a photographic darkroom must be greatly subdued and dispersed, and there again is no suggestion that the light passing through the polarized lenses could be projected as an incident beam of light to illuminate specific objects at a considerable distance.